Tech Tip

Tech Tip: TT707.007
Product: Series 707 Super Voyager VLB-III
Revision: Rev D
Frequency: All frequencies
Date: February 27, 1995
Originator: Vivek Saxena
Released By: Documentation Control

Subject: LED Problem

Problem: The Power LED blinks when the modem/mouse is used.

Reason: On the series 707, the power LED is also driven by the
"Password LED" logic. There is some noise on the password
LED signal, and it is this noise which is seen on the
power LED.

The following logic is implemented on the motherboard:

When the Keyboard is locked, by using the <CNTRL><ALT><BACK-SPACE> sequence,
the Num lock, Caps Lock, Scroll Lock keys on the keyboard all blink,
indicating that the keyboard is locked.

At the same time, the user can also select another LED to
blink in this condition. There are two choices for this LED:

1. Use the System Power LED. In this case, the
power LED will blink when the keyboard is locked. This is chosen by
selecting 1-2 on J39.

2. Use a separate LED. In this case, the user will
have to connect a LED to J38 and select 2-3 on J39.

The boards are shipped in configuration #1. We have
observed some noise on the Password LED signal. Since the password LED
signal is wired-ored with the power LED, the noise can be seen on the
power LED.

Solution: Do not use option #1 above. Change J39 to 2-3, and if
needed, connect an external LED to J38.